Sepsis and severe inflammatory response syndromes are caused by an over-reaction of the immune system to invasive pathogens. Pathogen-derived microbial pattern recognition motifs activate transmembrane receptors of the Toll-Like-Receptors and Interleukin-1Receptor (TLR/IL-1R) superfamily to mount an inflammatory response of the innate immune system. TLR/IL-1R members initiate intracellular signaling cascades required for host defense by recruiting Myeloid Differentiation factor 88 (MyD88) and MyD88-like adaptor proteins at their intracellular regions. However, uncontrolled activation of the innate immune system can lead to systemic inflammation and excessive collateral damage to host tissues. The IL-1 signaling pathway plays a preeminent role in systemic inflammatory response syndromes and can directly cause widespread endothelial dysfunction, progressive multi-organ failure and death. This proposal intends to modify the immune response and limit collateral damage to the host by blocking the signaling adaptor MyD88. Specifically, MyD88 binds to TLR /IL-1R through its Toll Interleukin Receptor (TIR) domain. The interacting surfaces on the TIR domain of the adaptor and the receptors consist of a conserved hydrophobic sequence (F/Y)-(V/L/I)-(P/G) in a 2-strand conformation. We propose to interfere with MyD88-dependent signaling using synthetic analogues of this interface, called BB-loop mimetics. Lead molecules, with confirmed activity in animal models of fever and LPS- induced acute lung injury, are already in hand and show in vivo efficacy toward the IL- 12 signaling cascade. We propose to further develop these for intervention in systemic inflammatory response syndromes and sepsis: Aim1 is to synthesize a library of low molecular weight MyD88-TIR domain mimetics in a structure-based approach;Aim 2 is to further characterize these compounds in cellular models to establish inhibitory selectivity towards TLR/IL-1R signaling;and to examine and optimize pharmacokinetic properties of selected lead compounds;Aim 3 is to test the potency of lead compounds in preventing lethal systemic inflammatory response syndromes and sepsis. These studies intend to establish a new principle for modifying innate immune signaling through targeting the central adaptor interface of the TLR/IL1R superfamily with small, synthetic compounds. The broader goal is to interrupt inflammatory exacerbation and prevent death in animal models of sepsis. PUBLIC HEALTH RELEVANCE: Sepsis and severe inflammatory response syndromes are caused by an over- reaction of the immune system to invasive pathogens. This research proposes to use small, synthetic compounds to attenuate the immune response. A collection of molecules will be synthesized, tested in cell lines and optimized for their activity in the treatment of sepsis in appropriate animal models.